Measuring efficiency of bioluminescent bacteria

I want to run an experiment to try and experimentally determine the efficiency (as in what percent of energy is converted to light) of bioluminescent bacteria (V. Fischeri), and compare it to the efficiency of a "traditional" light source, like an LED or an incandescent.

I know how I would determine the efficiency of an electrical source (measure the temperature of the source, turn it on, measure the temperature again after a set time, and use a couple of equations to determine energy lost as heat over energy consumed), but I am stuck on how I would measure the efficiency of a bacteria culture. The same temperature idea might work to determine the waste heat, but how would I find total energy consumed (or energy emitted as light)?

If you can measure the energy consumed by the bacteria both when they are 'dark' and when they are 'light', you know how much energy is being used to generate light (as opposed to overall metabolic expenditures). Then, if you measure the radiated power (you would need to measure the spectral intensity), you have the efficiency.

But- how to measure the energy consumed? I guess you could culture the bacteria in a calorimeter and measure the heat: